There is considerable interest in developing chemically sensitive sensors that are capable of detecting and identifying a particular chemical analyte by a detectable response. In certain instances, these sensors are incorporated into artificial olfactory devices or electronic noses that are capable of detecting a wide variety of analytes in fluids such as vapors, gases and liquids. Typically, the electronic nose (e-nose) device comprises an array of sensors that in the presence of an analyte produces a response. The device produces a unique signature output for a particular analyte. Using pattern recognition algorithms, the output signature, such as an electrical response, can be correlated and compared to a particular analyte or mixture of substances that are known. By comparing the unknown signature with the stored or known signatures, the analyte can be detected, identified and quantified.
Certain sensor types have polymeric components. Such organic polymer-based sensors have found use in a variety of different applications and devices including, for example, devices that function as analogs of the mammalian olfactory system (see, U.S. Pat. No. 5,571,401, which issued to Lewis et al., Lundström et al., Nature 352:47-50 (1991) and Shurmer and Gardner, Sens. Actuators B 8:1-11 (1992)), bulk conducting polymer films (Barker et al., Sens. Actuators B 17:143 (1994) and Gardner et al., Sens. Actuators B 18:240 (1994)), surface acoustic wave devices (Grate et al., Anal. Chem. 67:2162 (1995), Grate et al., Anal. Chem. 65:A987 (1993) and Grate et al., Anal. Chem. 65:A940 (1993)), fiber optic micromirrors (Hughes et al., J. Biochem. and Biotechnol.41:77 (1993)), quartz crystal microbalances (Chang et al., Anal. Chim. Acta 249:323 (1991)) and dye impregnated polymeric coatings on optical fibers (Walt et al., Anal. Chem. 68:2191 (1996)).
U.S. Pat. No. 5,756,879, which issued to Yamagishi et al., on May 26, 1998, discloses a sensor comprising (a) a dielectric substrate having a surface; (b) a pair of electrically conductive electrodes disposed on the surface of the substrate; and (c) a conductive polymer covering the pair of electrically conductive electrodes, with the conductive polymer doped with appropriate dopants to change the conductive polymer from a neutral state to a charged state to provide requisite conductivity. The sensors as taught therein are limited to coating with conducting polymer sensors.
U.S. Pat. No. 5,945,069, which issued to Buehler, on Aug. 31, 1999, discloses a gas sensor test chip that utilizes a variety of electrode geometries to generate varied responses to selective gases. The gas sensor is fabricated on a substrate that includes a plurality of electrodes where each electrode has a plurality of shapes and dimensions. Polymer films are deposited over the electrodes. The polymer films have a conductivity that changes when the film is exposed to various gases as measured across the electrodes. An optimal geometric configuration for the electrode is selected based on prior tests of the film's response to various gases of interest.
WO 99/49305, published Sep. 30, 1999, discloses a method of manufacturing a batch of sensors by electrochemically depositing an active sensing material over the substrate and conductive tracks, wherein the conductive tracks are part of a single circuit, the active sensing material is then removed from a predetermined portion of the substrate and thereafter the substrate is subdivided to produce a plurality of sensors.
What is needed in the art is a process for depositing a sensor onto a substrate wherein the sensor comprises multiple layers. The present invention remedies such need.